We know little about projections of the primate cerebellar cortex, and almost no attempt has been made to correlate the evolution of upright primate locomotor styles with specializations of cerebellar connectivity. This study will address both of these points. The animal models utilized are the lesser bushbaby (Galago senegalensis) a Lorisoid primate with a unique upright locomotor style and the tree shrew (Tupaia glis) a generalized quadrupedal mammal considered to be the best extant example of the Paleocene form from which primates evolved. An in-depth analysis of cerebellar corticonuclear connections, using the Fink-Heimer selective silver impregnation method, will be completed. Special attention is directed to the topographical representation of the cortex in the deep nuclei and the organization of zones in the cortex as reflected by the arrangement of this fiber system. Using horseradish peroxidase (HRP) as a retrograde tracer, the location and organization of nucleocortical cells will be ascertained. Emphasis will be placed on their topographical relationship with the ipsilateral cortex, and on the distribution of the recently discovered contralateral nucleocortical cells. Cerebellar nuclear efferent projections to select brainstem relay nuclei (e.g. red nucleus, vestibular nuclei, pontine nuclei) and the specific population of cells of the nucleus dorsalis which gives rise to spinocerebellar fibers will both be studied using HRP methodology. In the former HRP injections will be stereotaxically placed and in the latter a special concern will be the laterality of these cells in relation to injection sites. The anterograde course and termination of spinocerebellar fibers in sagittally oriented laminae in the granular layer of the cerebullar cortex will be determined using Fink-Heimer method. An integral part of this proposal is a series of Golgi studies which will elucidate the organization of terminal nuclei. The results will be considered in light of the phylogentic level and locomotor style of each species and current theories concerning locomotor evolution in primates.